Color filters are used for liquid crystal displays (LCDs), optical filters for cameras, and the like. Color filters may be manufactured by coating a fine region colored with three or more colors on a charge coupled device or a transparent substrate. This colored thin film can be manufactured using a method of dyeing, printing, electrophoretic deposition (EPD), pigment dispersion, and the like.
The pigment dispersion method forms a colored film by repeating a series of processes such as coating, exposing to light, developing, and thermally curing a photopolymer composition including a colorant on a transparent substrate including a black matrix. This method may improve heat resistance and durability, which are very important characteristics for a color filter, and may provide a uniform film thickness. For example, Korean Patent Laid-Open No. 1992-7002502, Korean Patent Laid-Open No. 1995-7000359, Korean Patent Publication No. 1994-0005617 and Korean Patent Laid-Open Publication No. 1995-0011163, and the like disclose a method of manufacturing a photosensitive resin composition for a color filter using a pigment dispersion method.
The color filter is prepared through many chemical treatments during the manufacturing process. Accordingly, in order to maintain a pattern formed under the aforementioned conditions, a color photosensitive resin is required to have a development margin but chemical resistance to improve yield of a color filter.
In particular, a conventional color liquid crystal display (LCD) is generally fabricated by preparing a color filter substrate for displaying a color image differently from an operating substrate on which TFT is disposed and then binding the color filter substrate and the operating substrate together. However, since they have low arrangement accuracy during the binding, they require a shading layer with a large width. Accordingly, it is difficult to increase its aperture ratio (a ratio of an opening to transmit light).
Also, as the glass substrates of LCDs and LCD screens have recently become larger, it takes a longer time for a liquid crystal composition to be disposed over the front side of the substrates during vacuum injection of a liquid crystal. Accordingly, a new method has been suggested to sharply decrease the time needed for printing a seal material and dripping a liquid crystal for over-coating; this method, however, has a problem of sharply deteriorating arrangement accuracy.
On the other hand, another method of forming a color filter on the operating TFT array substrate of a TFT color liquid crystal display (LCD) has been suggested. Since this method does not need a color filter substrate and by fabricating a transparent substrate through sputtering and binding two substrates, it has an advantage of simplifying arrangement and increasing an aperture ratio. However, when a color filter is formed on a TFT array substrate, a pixel electrode is formed on the color filter in a photolithography method by using a common positive photoresist. Accordingly, the resist layer needs to be removed after forming the electrode. In other words, a pixel electrode is formed by forming a transparent electrode layer on color pixels of a color filter, coating a positive resist composition thereon, and patterning it, exposing it to light, and developing it. Then, the resist layer remaining on the pixel electrode should be peeled and removed with a resist stripper. Accordingly, the positive resist composition requires resistance for the resist stripper.
A conventional photosensitive resin composition has weak resistance for a resist stripper. According to the conventional art, a pixel electrode is fabricated by forming a transparent layer (a pixel protective layer) having stripper-resistance on a color filter. In addition, a pixel electrode may be manufactured without coating a pixel protective layer by treating a stripper at a low temperature for a longer time to decrease the stripper's influence on a color filter. However, these conventional methods have problems of deteriorating yield rate and production efficiency, since more processes and longer times are required. In particular, the conventional methods can require longer baking times at a high temperature, which can deteriorate a color shift or luminance and can severely shrink a pattern as the pattern is constantly cured by heat.
Accordingly, there is a need for a photosensitive resin composition for manufacturing a color filter having excellent heat resistance and a low shrinkage ratio.